The present invention pertains generally to a pressure sensor and, more particularly, to a corrosion-resistant diaphragm pressure sensor used for liquid chemical containers, liquid chemical piping, etc.
In general, a diaphragm pressure sensor is constructed in such a way as to sense pressure by converting the displacement of a diaphragm generated by pressure applied to the diaphragm into an electronic signal. In particular, a diaphragm pressure sensor for sensing pressure of strong acid, strong alkaline liquid chemicals, etc. conventionally has had a diaphragm. The surface of the diaphragm can be coated with fluoroplastics, if the diaphragm is made of metal, or the diaphragm can be made of a highly corrosion-resistant material such as alumina ceramic, etc. with a view to minimization of corrosion by liquid chemicals such as mentioned above.
However, a metal diaphragm coated with fluoroplastics employed in a conventional diaphragm pressure sensor has a limited life due to poor uniformity of coating, pinholes, etc. Further, a diaphragm made of alumina ceramic, although it has satisfactory corrosion resistance properties, slightly dissolves in strong acid or strong alkaline liquid chemicals.
It is an object of the present invention to provide an improved diaphragm pressure sensor for sensing fluid pressure, characterized by excellent corrosion resistance to strong acid, strong alkaline liquid chemicals, etc.
A diaphragm pressure sensor of the present invention comprises a pressure guide member made of fluoroplastics for the admission of liquid chemicals, pressure of which is measured, and a pressure frame made of perfluoroalkoxy resin (pheno-lformaldehyde) integrated with the pressure guide member to constitute a container for holding the liquid chemicals. A ceramic diaphragm is provided for housing a pressure sensor portion, which is bonded to the surface of the pressure frame opposite to the surface against which pressures of the liquid chemicals are applied. A body houses the pressure guide member, pressure frame and diaphragm.
Since a diaphragm pressure sensor of the present invention does not have an O-ring, etc. as an airtight seal for liquid chemicals installed between a ceramic diaphragm housing a pressure sensor part and a liquid contact portion, it is free from leakage of liquid chemicals caused by deterioration of an O-ring, etc. Therefore, the diaphragm in the present sensor can be fully protected from highly-corrosive liquid chemicals.
Further, a pressure guide member made of perfluoroalkoxy resin and a pressure frame also made of perfluoroalkoxy resin in the present invention are integrated such that they form a single component made of perfluoroalkoxy resin. Therefore, the present sensor can achieve excellent corrosion-resistance to strong acid, strong alkaline liquid chemicals, etc.